EUV Mask Edge Detection Using Dual-Axis Illumination
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Solution Overview
Problem
Current position detection methods for EUV masks are inefficient in accurately detecting the edge position due to particle adhesion issues and are influenced by the shape of the substrate edge, leading to low precision and errors in positioning, especially when using removable pellicles and cover-like structures.
Innovation Solution
A position detecting apparatus and method that uses dual illuminating units to radiate light onto the substrate from different directions, allowing for precise edge position detection by taking images from the rear surface and calculating edge positions based on intensity profiles, thereby minimizing the impact of substrate edge shape and particle adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a removable pellicle is used to protect the EUV mask, then particle adhesion is reduced, but positioning precision deteriorates due to contact with supporting pins or pads
Solution Approach 1:
The patent replaces mechanical contact-based positioning with optical field-based positioning. Instead of using supporting pins or pads that physically touch the mask substrate, the invention uses a projection optical system to detect the mask position by projecting a beam and detecting its position on the mask surface, thereby eliminating mechanical contact and associated particle generation while maintaining high positioning precision
Solution Approach 2:
The patent introduces an optical field as an intermediary between the positioning system and the mask substrate. The projection optical system creates a light field that interacts with the mask without physical contact, allowing position detection through optical means rather than mechanical contact, thus preventing particle adhesion while achieving accurate positioning
2Strength
If mechanical supporting pins or pads are used in removable pellicles, then the mask can be held securely, but particle generation increases due to contact and friction
Solution Approach 1:
The patent replaces the mechanical supporting pins or pads with an optical field-based positioning and holding system. The projection optical system can detect and maintain mask position without physical contact, eliminating the friction and particle generation associated with mechanical contact while maintaining secure mask holding capability through optical feedback and control
3Object-affected harmful factors
If the EUV mask is transported while attached to a removable pellicle, then protection is maintained, but particle occurrence increases due to rubbing between mask and pellicle
Solution Approach 1:
The patent replaces mechanical contact-based transportation with optical field-based positioning and support. During transportation, the projection optical system continuously monitors and maintains mask position without physical contact, eliminating rubbing between mask and pellicle while maintaining protection and transportation convenience through non-contact optical control
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution achieves high precision in detecting edge positions with improved accuracy and reliability, even when EUV masks are attached to or detached from removable pellicles, reducing particle adhesion and positional errors.
Implementation Method 1
a first illuminating device that radiates light onto a substrate in a direction substantially parallel to a front surface and a rear surface of the substrate from a lateral face of the substrate
Implementation Method 2
a second illuminating device that radiates light onto an area that includes an edge portion of the substrate in a direction substantially perpendicular to the front surface of the substrate from above the front surface of the substrate
Implementation Method 3
an image pickup device that takes a first image and a second image
Data Source
AI summary
A position detecting apparatus includes a first illuminating unit that radiates light onto a substrate in a direction substantially parallel to the front and the rear surfaces of the substrate from the direction of a lateral face of the substrate; a second illuminating unit that radiates light onto the front surface of the substrate, in a direction substantially perpendicular to the front surface of the substrate; an image pickup unit that takes an image of the substrate from a rear surface side thereof; and an edge-position detecting unit that detects an edge position of the substrate, based on a first image that is taken while the light is being radiated from the first illuminating unit and a second image that is taken while the light is being radiated from the second illuminating unit, respectively.